1. Field of the Invention
The present invention relates to a gettering substrate for reducing a pixel defect generated by a heavy metal impurity in a solid-state image pickup device such as a CMOS image pickup device, a semiconductor substrate for a solid-state image pickup device, and a producing method therefor.
2. Related Background Art
It is already known that, in a semiconductor device manufacturing process, characteristics of the device are deteriorated when a crystalline defect, generated by a contamination by a heavy metal such as Fe, Ni, Cr etc. present in a semiconductor substrate, is formed on a surface of the semiconductor substrate on which a device is to be formed.
In particular, in a CMOS image pickup device, a crystalline defect generated in a photoelectric converting device generates a weak current in a dark state, causing a white dot defect in the image pickup device.
For reducing such white dot defect, there has been employed an IG (intrinsic gettering) method or a PBS (polysilicon back seal) method.
The IG method is described for example in Japanese Patent Application Laid-open No. H11-021200, and the PBS is described for example in Japanese Patent Application Laid-open No. H07-022429 (corresponding to U.S. Pat. No. 5,419,786).
Also in order to avoid a drawback of excessive BMD (bulk micro defect) generation in the PBS method, Japanese Patent Application Laid-open No. H08-045944 describes a temperature defining prior to a polysilicon film formation on the rear surface, and Japanese Patent Application Laid-open Nos. H08-104592 and H11-103042 describe that an impurity introduction leads to a dark current generation and a white dot defect in the semiconductor image pickup apparatus.
It is also known that an output of the white dot defect in the image pickup apparatus depends on a type of heavy metal constituting the cause thereof.
For gettering of such various heavy metals, the IG method and the PBS method are useful.
However, a single gettering technology is insufficient for achieving a gettering effect for plural heavy metals.
This is because each heavy metal has a matching gettering technology. FIG. 5 briefly shows an example.
It is shown that the PBS method is more effective than the IG method for a certain output, and the IG method is more effective for other output.
Therefore, for reducing the number of white dot defects thereby improving the image obtained by the image pickup apparatus, there is desired a gettering technology effective for various heavy metals constituting the cause of such defects.